How to access the bundled Python executable for subprocess in Blender scripts?
The path to access this is bpy.app.binary_path_python

The exact details on how you should run the process are up to you, and not Blender spesific.

Best try the subprocess module, but os.system will work too.

Heres a very simple example calling a Python sub-process.

import bpy
import subprocess
import time

command = (
    bpy.app.binary_path_python,
    "-c", "import time; time.sleep(2)",
    )
proc = subprocess.Popen(command)

while proc.poll() is None:
    print("Waiting...")
    time.sleep(0.1)

print("Finished with exit code %d" % proc.returncode)


For an example of how to run Python as a subprocess without locking up Blender, see this Q &amp; A.